The present invention pertains to a system for fabricating septic tanks.
Septic tanks typically must be built to conform to regulations promulgated by one or more respective governmental entities such as state governments, city governments and other such municipalities, etc. These governmental regulations seek to ensure that septic tanks used in commercial or residential construction are structurally sound and are accessible for maintenance. For example, many jurisdictions have standards setting the amount of fluid pressure that commercial and residential septic tanks must be capable of withstanding. Conformance with these standards is usually tested by filling a finished septic tank with an amount of water sufficient to provide the pressure that the septic tank must be built to withstand.
Existing concrete septic tanks are typically formed by pouring concrete into an outer mold, and around an interior plug positioned within the mold. In order to facilitate the bulk fabrication of septic tanks, it is desired that both the outer mold and the inner plug be reusable to permit multiple concrete castings, thus reducing the cost of fabricating septic tanks. For example, U.S. Pat. No. 3,990,673 to Jones et al. and U.S. Pat. No. 3,687,597 to Lavergne Jr. each disclose respective reusable systems in which the inner plug and the outer mold may be detached from the hardened concrete septic tank. Though detachment of the outer mold from the hardened concrete is easily accomplished, detachment of the inner plug is often complicated. First, to facilitate removal of the plug from the interior of the hardened concrete casting, only five sides of the septic tank are poured using the aforementioned mold and plug assembly, with the remaining side poured separately, as will be later described. Once the concrete surrounding the plug has hardened, the plug must be detached from the five faces of the concrete tank and removed through the open side. Detachment of the plug from the concrete casting in which it is encased may involve either overcoming a substantial amount of friction generated over the large surface area where the plug and the concrete press against each other, or alternatively, some systems, such as the aforementioned patent to Jones et al., employ a complicated structure by which the inner mold is collapsed inward, and away from the concrete walls to avoid the resisting friction on the plug.
Once the plug has been removed, a cover (or top) of the septic tank is secured to the remainder of the tank enclosure. The cover is typically formed by pouring concrete into another mold that provides for an opening through the cover so that the interior of the finished septic tank may be accessed for maintenance.
Unfortunately, pouring a septic tank using the previously described prior art reusable mold and plug systems produces a finished septic tank that often fails to meet the required standards for fluid pressure containment. Specifically, when the tanks are tested by filling them with water to a required pressure, leakage occurs at the junction between the cover and the poured five-sided enclosure. Essentially, the economic incentive to reuse a plug, which dictates that the poured enclosure have an open side for removing the plug, weakens the septic tank structurally at the connection between that poured enclosure and the separately-poured cover.
What is desired, then, is a system for pouring septic tanks that includes a reusable plug and that produces a poured septic tank having improved structural strength over septic tanks fabricated using existing systems.
The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.